Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and somatomedin C (SmC) can be employed to study the initiation of growth, G0/G1 traverse, and commitment to DNA synthesis. PDGF initiates cellular proliferation of density-arrested fibroblasts, whereas other growth factors facilitate the traverse of the cell cycle. Since transformation abrogates the PDGF requirement, it is important to determine how PDGF functions and how transformation alters this function. Proteins induced by PDGF that may be involved in growth initiation will be studied and characterized. Polyacrylamide gel electrophoresis will be used to identify these proteins. EGF will also be used to study induced proteins to determine if EGF and PDGF stimulate proliferation via the same mechanism. The proteins whose synthesis is normally regulated by PDGF that are constitutively synthesized in transformants will be characterized. The mechanism of action of somatomedin C is proposed to be a post-transcription process. This mechanism will be investigated. A series of PDGF-regulated genomic sequences will be isolated in order to develop the time sequence of PDGF-inducible genes. This isolation will employ standard cloning techniques. The isolated PDGF-inducible sequence will be studied to determine if they share homology with known oncogenes. A long-term objective is to develop PDGF-inducible DNA sequence in an expression vector. The ability for PDGF to stimulate synthesis of glycoprotein or proteoglycans will be investigated and related to growth initiation. These studies are designed to allow a better understanding of cell cycle regulation. A development of monoclonal antibodies to PDGF is also planned. Standard technique will be employed to screen possible anti-PDGF Ab-producing hybridomas. (N)